The present invention relates to a new and improved apparatus for fault direction-comparison protection of electrical lines, in particular containing at least one series capacitor or capacitance. At both ends of a line section to be protected there is provided a respective measuring monitoring station having a fault direction detector and between both of these stations there is arranged a transmission channel for fault direction data. Additionally, there is provided at least one comparison-evaluation device for the fault site determination with respect to the line section to be protected.
Such type equipment is known, for instance, from the publication of L. Muller, entitled "Selektivschutz electrischer Anlagen", Verlags- und Wirtschaftsgesellschaft der Electrizitatswerke m.b.H., Frankfurt/Main, 1971, page 89, and delivers a trip signal in those instances where the fault direction signals at both end stations of the line section to be monitored are directed towards the same.
For the present fields of use which are contemplated i.e. for sectionalizing or narrowing the fault site with respect to a line section, conventional directional relays of simple construction are afflicted with the drawback that there is a relatively great probability of faulty tripping in the case of near faults or short-circuits at the rear side of a measuring and monitoring station, in other words externally of the line section to be protected. This is especially so for lines or network sections having a series capacitor or a number of such capacitors or capacitances due to the pronounced transient oscillations which are formed upon failure or non-response of the standard shunt switches or protective gap at the series capacitors. Such non-response of the protective gap often cannot be avoided when encountering relatively low fault currents.